If it's streaming video, it just may be network lag.
I personally end up having all sorts of problems with WMP10, so I generally just don't use it much if I don't need to. Hell if I know why PC Magazine rated it so favorably.
WMP 10 is simply a turd. Horrible piece of software... constant problems, one of my favourites being looping clips that move at around -10fps after the first play.
